The overall UW ACE theme centers on a comprehensive developmental model of risk, risk processes, symptom emergence, and adaptation in autism spectrum disorder (ASD). According to this model, early autism risk factors (genetic/familial and environmental) lead to risk processes, namely altered patterns of interaction between the child and his/her environment, which contribute to the abnormal development of neural circuitry and atypical behaviors. By identifying infants at risk at an early age when the brain is developing and before core autism symptoms have emerged, it might be possible to alter the developmental trajectory of children at risk for the disorder and have a significant impact on long-term outcome. Both clinical progress and basic science will profit from the identification of endophenotypes [unreadable] intermediate, quantifiable traits that predict an individual's risk of having a disorder, which can be linked to underlying cause. The goals of Project II are two-fold: First, in a sample of infant sibs, we aim to investigate whether neurophysiological risk indices (endophenotypes) measured at 6-7 mos of age will improve our ability to identify infants who will develop autism or autism-related symptoms by age 2. Second, we will assess whether it is possible to alter risk processes via early intervention with high-risk infants, thereby reducing severity of autism symptoms. Specifically, we plan to investigate the efficacy of early intervention that is designed to enhance early social responsiveness and communication in infants who are at risk for autism (infant siblings of children with autism). Despite the fact that our ability to identify infants at risk for autism is rapidly improving, early interventions for infants at risk for autism have not yet been tested. This project represents a first step toward developing effective interventions for at-risk infants. The proposed work on early autism risk factors will have impact on several key areas: (1) Identification of the biological and/or behavioral risk indices in infancy, for the development of autism and autism- related symptoms, such as language and social impairments; (2) development of intervention methods for infants and toddlers to lower the age for which there are efficacious interventions; (3) identification of individual characteristics that predict response to behavioral treatment; and (4) provision of evidence that cases of autism might be secondarily prevented through early identification and early treatment.